Free cutting alloys



, of copper have a wide range of usefulness because of their favorable mechanical properties Patented Jan. 7, 1936 PATENT "OFFICE" FREE CUTTING ALLOYS Louis W. Kempf and Walter A. Dean, Cleveland, Ohio, assignors to Aluminum Company of America, Pittsburgh, Pennsylvania Pa., a corporation of No Drawing. Original application September 18,

1933, Serial No. 689,877.

Divided and this application May 3, 1935, Serial No. 19,606

2 Claims.

The invention relates to aluminum base alloys and is particularly concerned with alloys of this nature containing substantial amounts of copper.

This application is a division of our co-pending application Serial No. 689,877, filed Septemr ber 18, 1933. Alloys disclosed but not claimed herein are claimed in our above mentioned copending application Serial No. 689,877 and our co-pending applications Serial Nos. 19,604 and 19,605, filed May 3, 1935.

Despite the manifold advantages connected with the use of aluminum and its alloys in commercial fields, there is an inherent drawback which somewhat curtails their use'incertain potential adaptations. Aluminum alloys, for instance, containing from about 4 per cent toabout 12 per cent and their susceptibility to improvement by suitable thermal treatments. Mechanical cuttingoperations, however, such as boring, drilling,

planing, or lathe-cutting'are successfully car-.

' ried out only by using certain precautions which increase the expense of the operation and which occasionally necessitate the substitution of another alloy which may be machined more readily but which is otherwise not so'desirable from the standpoint of physical properties. When alloys are diflicult to machine this'disadvantage be-' comes evident, in many cases, through rapid wear of the cutting'tool edge which necessitates fre-- quent resharpening. In such cases where machining is diflicult, continual lubrication is required; the machined surface is rough and irregular, and the chip has a tendency to form continuous curls or spirals that may foul the tool or the operating parts of the machine. These drawbacks retard production and increase the cost of operation. Many articles require a variety of machining operations before being applied to their final purpose and it is particularly desirable that these articles be finished economically and satisfactorily.

An object of this invention, therefore, is the production of alloys which may be readily machined and which contain substantial amounts of copper. v

, A further object is the'production of such a1- loys whose mechanical properties in the preferred composition range are perfectly adequate to suit most commercial purposes.

These objects we have effected by the addition to aluminum-copper-cadmium alloys of at'least one of the elements lead, bismuth or thallium.

4 per cent to about 12 per cent of copper, forms.

a particularly desirablebase alloy to which can be added one or more of the alloying elements lead, bismuth, or thallium. The lead may be present in amount between about 0.1 per cent and 10 per cent, the bismuth between about 0.05

per cent and 1.5 per cent, and the thallium between about 0.05 per cent and 3 per cent. These added elements, in combination with cadmium in aluminum-copper alloys, have a very favorable effect on the machining properties 'of the alloys. In this sense the elements cadmium, ,lead, bismuth, and thallium may be termed free machining constituents," just as the alloys they form are now called free machining alloys, to indicate the fact that they may be machined more rapidly, and with a chip which flows more freely from the tool leaving a cleaner machined surface than similar alloys not containing the cadmium, bismuth, lead, or thallium.

Cadmium within the above disclosed range effects an increase in the tensile strength, shear strength, and Brinell hardness of the aluminumcopper alloys while the elongation is caused to drop off correspondingly. The remaining constituents, namely, lead, bismuth, or thallium, appear not to materially afiect the mechanical properties of the aluminum-copper alloys except in so far as they are. beneficial to the machining properties. We have found that when the cadmium is used in combination with one or more of the other free machining elements lead, bismuth or thallium, the advantageous effect of the cadmium on the tensile strength, shear strength, and harness of the aluminum-copper alloys is not diminished materially whereas the machining properties of the resulting alloys are very materially accentuated.

The simultaneous presence of more than one of the disclosed free machining elements is more advantageous than that of the same total amount of either of the elements used separately. If, for

' instance, weare working with an aluminum base alloy containing-about 6 per cent of copper and 1.0 per cent of cadmium, and in a particular ap-= 1o e be added by introducing these constituents in the cadmium, it is more advantageous to make up this 1.5 per cent by using more than one of the constituents lead, bismuth, or thallium, than to. add 1.5 per cent of one element alone. In conformity with the same principle, the addition of one of the elements lead, bismuth, or thallium to the aluminum-copper alloys in which cadcadmium alloys we prefer to use about 1.0 per cent of the element. As a preferred base alloy we use an aluminum alloy containing 6.0 per cent of copper and 0.25 per cent of cadmium. If more than one of the elements lead, bismuth, or thallium is to be added to an aluminum-.copper-cadmium alloy the preferred amount of free machining elements, inclusive of the cadmium, should be about 1.0 per cent, although amounts in excess of this composition: and up to the total amount of each disclosed hereinbefore, continue to exert a beneficial effect on the cutting properties of the alloy. The preferred limit of 1.0 per cent of total free machining constituent represents a point at which'the mechanical properties and the machining properties of the alloy reach a most favorable balance although of course there may be many commercial applications wherein improved machining characteristics caused byfurther additions of free cutting constituents may more than compensate for the lowering of mechanical properties.

The lead, thallium, cadmium, and bismuth may num.

solid form into a molten heat of the aluminum base alloy since they melt at a temperature considerably below those customarily encountered in the commercial handling of molten aluminum or its alloys in the foundry. Since the specific gravity of the free machining elements is con-, siderably higher than that of aluminum, and their liquid solubility is limited, the melt should be heated somewhat above the ordinary temperature and stirred vigorously to assure a thorough mixture of the alloying constituent. The method of adding heavy low melting point metals to aluminum here referred to is more fully described in co-pending application Serial No. 689,885 now Patent No. 1,959,029, granted May 15, 1934.

The alloys herein disclosed may be subjected to the usual thermal treatments familiar to those skilled in the art of treating aluminum-copper alloys for the purpose of altering their physical characteristics.

The term aluminum as used herein and in the appended claims embraces the usual impurities found in aluminum ingot of commercial grade or picked up in the course of the usual handling operations incident to ordinary melting practice.

We claim:

1. An aluminum base alloy containing from about 4 to 12 per cent of copper, from about 0.05 to 1.5 per cent of cadmium, from about 0.1 to 10 per cent of lead, and from about 0.05 to 1.5 per cent of bismuth, the balance being aluminum.

2. An aluminum base alloy containing from about 4 to 12 per cent of copper, iroin about 0.05 to 1.5 per cent of cadmium, at least 0.1 percent of lead and at least 0.05 per cent of bismuth, the total lead and bismuth in the alloy not exceed-' ing about 1 per cent, the balance being alumi- LOUIS w. WALTER A. DEAN. 

